Red Gate's schema comparison tool, SQL Compare, is in beta for the newest version, SQL Compare 7. You can find details and a link to download here:
Red Gate Forums: SQL Compare 7 Beta
This version does include support for SQL Server 2008 (through CTP 6). The beta period will run through July 4, 2008, as SQL Compare 7 is scheduled to be released to manufacturing (RTM) during the 3rd quarter of 2008. If you're interested in taking a look at this new version and offering comments, please visit the link and download the trial version. If you already have SQL Compare 6, don't worry, the beta version of SQL Compare 7 will install beside it (I have both running in parallel). You will need the Microsoft .NET Framework 2.0 installed in order to use the product.